Eclogite and garnet pyroxenite xenoliths from kimberlite pipes of north Siberian craton - evidences of subduction processes and cumulate origin

2021 ◽  
Author(s):  
Tatiana Kalashnikova ◽  
Lidia Solov'eva ◽  
Sergey Kostrovitsky ◽  
Konstantin Sinitsyn ◽  
Elvira Yudintseva
Keyword(s):  
Mineral Composition ◽  
Siberian Craton ◽  
Lithospheric Mantle ◽  
Isotope Composition ◽  
Bulk Composition ◽  
Mantle Xenoliths ◽  
Rock Composition ◽  
Geochemical Properties ◽  
Eu Anomaly ◽  
Wide Range

<p>The lithospheric mantle structure and evolution is one of the fundamental problems of the Earth's history. Eclogites and clinopyroxenite xenoliths are characterized by a similar two-mineral composition (garnet and clinopyroxene), but differ in mineralogical and petrographic features (Gonzaga et al., 2010). Questions of their origin and relationship with peridotites remain controversial. There are several classifications of eclogites based on various attributes: structural and textural features (Mercier & Nicolas, 1975; MacGregor & Carter, 1970), chemical composition of garnet (Coleman, 1965), clinopyroxene (Taylor & Neal, 1989), as well as the whole rock composition (Aulbach et al., 2016 and other), the given classifications may not coincide. The geochemical properties of eclogite xenoliths from kimberlite pipes suggest two main points of view for genesis: implication of subduction processes or cumulates of high-pressure melting in lithosphere mantle (Condie, 1993; Jacob et al., 1994). The "classical" cratonic eclogites represent an ancient oceanic crust subsequently subducted and altered possible further metasomatic processes. These rocks are characterized by significant variations in the composition of minerals, a relatively high content of Al<sub>2</sub>O<sub>3</sub> (14-20 wt%) and a low MgO content (10-15 wt%), depletion of elements of the LREE and an Eu anomaly (Gonzaga et al., 2010). In addition, eclogites have a wide range of oxygen isotopic composition in garnet δ<sup>18</sup>O 4.51 - 8.69 (much higher than mantle values ​​5.3 ± 0.3) (9). Garnet pyroxenites are characterized by a more magnesian garnet - pyrope and bulk composition (MgO - 15-20 wt.%). The oxygen isotope composition of Grt from clinopyroxenites is close to that of the mantle - δ<sup>18</sup>O 5.2 - 5.8. It is assumed that these rocks are a consequence of the polybaric partial melting at high temperatures and pressures (Gonzaga et al., 2010). The mantle xenoliths from upper-Jurassic Obnajennaya kimberlite pipe (Kuoika field, Yakutia) were studied. Eclogites and clinopyroxenites occupy about 10-15% population among xenoliths. Garnet in the eclogites differs from that in the clinopyroxenites by a higher content of CaO and FeO (Prp<sub>55-62 </sub>Alm<sub>22-30</sub>Grs<sub>8-18 </sub>in clinopyroxenites and Prp<sub>40-45</sub>Alm<sub>13-29</sub>Grs<sub>15-30 </sub>in eclogites). Clinopyroxenes are distinguished by reduced magnesia content (Mg# 91-84), as well as low calcium content (16-18 wt.%). The high contents of jadeite components in the clinopyroxene (NaAl[Si<sub>2</sub>O<sub>6</sub>] - 25-32%) classify this group of rocks as eclogites. The high δ<sup>18</sup>O varies in eclogite Cpx (more than 6.0), positive Eu anomaly is assumed that the formation of the protolith of the xenolith group occurred as melts in the subduction zone during accretion of the Birekte block to the Siberian craton (Rosen, 2003). However, the presence of garnet clinopyroxenites with narrow variations in mineral composition and relatively low δ<sup>18</sup>O suggests melting processes in the lithospheric mantle and the formation of megacrystalline pyroxene cumulates.</p><p>The research was supported by Russian Science Foundation grant №20-77-00074.</p>

First noble gas results from fluid inclusions of the Late Miocene-Pleistocene Macedonian volcanics

2021 ◽  
Author(s):  
Kata Molnár ◽  
Marjan Temovski ◽  
László Palcsu
Keyword(s):  
Fluid Inclusions ◽  
Late Miocene ◽  
Lithospheric Mantle ◽  
Noble Gas ◽  
Mantle Xenoliths ◽  
Gas Composition ◽  
The European Union ◽  
Large Area ◽  
Development Fund ◽  
Wide Range

<p>Late Miocene to Pleistocene volcanism within the Vardar zone (N. Macedonia) covers a large area, has a wide range in composition and it is largely connected to the tectonic evolution of the South Balkan extensional system, the northern part of the Aegean extensional regime. A recent study indicated an increasing rate of mantle metasomatism towards the younger centers in the region [1]. During the last stage of activity, ultrapotassic (UK) centers that formed between ca. 3.2 and 1.5 Ma originated from the lithospheric mantle beneath the region [2]. Although there are no reported mantle xenoliths from these centers, the erupted mafic rocks contain abundant olivine as phenocrysts [3]. Noble gas isotopic characteristics of fluid inclusions in olivine can reveal important information about the origin of the fluid and the metasomatic state of the lithospheric mantle. We analyzed for the first time the noble gas composition of fluid inclusions of olivine phenocrysts from the Mlado Nagoričane volcanic center, the northernmost member of the UK centers with an eruption age of 1.8 ± 0.1 Ma [2]. The R/R<sub>A</sub> ratios give a range of 3.1-4.5 with <sup>4</sup>He/<sup>20</sup>Ne values of 11.7-14.6. These R/R<sub>A</sub> values are lower than the MORB and the averaged subcontinental lithospheric values, and considering the negligible amount of atmospheric contribution, imply a more metasomatized character for the underlying lithospheric mantle beneath the region. Mantle-derived noble gases were detected in a recent geochemical study on the thermal springs and gas exhalations in the region, with up to 20% of mantle contribution calculated based on their noble gas composition using the MORB R/R<sub>A</sub> value [4]. These new Mlado Nagoričane fluid inclusion noble gas values indicate that the mantle contribution in the recent gas emissions in the region could be higher than what was thought.</p><p>This research was supported by the European Union and the State of Hungary, financed by the European Regional and Development Fund in the project of GINOP-2.3.2-15-2016-00009 ‘ICER’ project</p><p>[1] Molnár et al. 2020 – EGU2020-13101.</p><p>[2] Yanev et al., 2008 – Mineralogy and Petrology, 94(1-2), 45-60.</p><p>[3] Yanev et al., 2008 – Geochemistry, Mineralogy and Petrology, Sofia, 46, 35-67.</p><p>[4] Temovski et al. 2020 – EGU2020-2763.</p>

scholarly journals Lithosphere tearing along STEP faults and synkinematic formation of lherzolite and wehrlite in the shallow subcontinental mantle

Solid Earth ◽  
2019 ◽  
Vol 10 (4) ◽  
pp. 1099-1121 ◽  
Author(s):  
Károly Hidas ◽  
Carlos J. Garrido ◽  
Guillermo Booth-Rea ◽  
Claudio Marchesi ◽  
Jean-Louis Bodinier ◽  
...  
Keyword(s):  
Grain Size ◽  
Lithospheric Mantle ◽  
Volcanic Field ◽  
Mantle Xenoliths ◽  
Coarse Grained ◽  
Fault System ◽  
Mantle Flow ◽  
Second Phase ◽  
Fine Grained ◽  
Wide Range

Abstract. Subduction-transform edge propagator (STEP) faults are the locus of continual lithospheric tearing at slab edges, resulting in sharp changes in the lithospheric and crustal thickness and triggering lateral and/or near-vertical mantle flow. However, the mechanisms at the lithospheric mantle scale are still poorly understood. Here, we present the microstructural study of olivine-rich lherzolite, harzburgite and wehrlite mantle xenoliths from the Oran volcanic field (Tell Atlas, northwest Algeria). This alkali volcanic field occurs along a major STEP fault responsible for the Miocene westward slab retreat in the westernmost Mediterranean. Mantle xenoliths provide a unique opportunity to investigate the microstructures in the mantle section of a STEP fault system. The microstructures of mantle xenoliths show a variable grain size ranging from coarse granular to fine-grained equigranular textures uncorrelated with lithology. The major element composition of the mantle peridotites provides temperature estimates in a wide range (790–1165 ∘C) but in general, the coarse-grained and fine-grained peridotites suggest deeper and shallower provenance depth, respectively. Olivine grain size in the fine-grained peridotites depends on the size and volume fraction of the pyroxene grains, which is consistent with pinning of olivine grain growth by pyroxenes as second-phase particles. In the coarse-grained peridotites, well-developed olivine crystal-preferred orientation (CPO) is characterized by orthorhombic and [100]-fiber symmetries, and orthopyroxene has a coherent CPO with that of olivine, suggesting their coeval deformation by dislocation creep at high temperature. In the fine-grained microstructures, along with the weakening of the fabric strength, olivine CPO symmetry exhibits a shift towards [010] fiber and the [010] and [001] axes of orthopyroxene are generally distributed subparallel to those of olivine. These data are consistent with deformation of olivine in the presence of low amounts of melts and the precipitation of orthopyroxenes from a melt phase. The bulk CPO of clinopyroxene mimics that of orthopyroxene via a topotaxial relationship of the two pyroxenes. This observation points to a melt-related origin of most clinopyroxenes in the Oran mantle xenoliths. The textural and geochemical record of the peridotites are consistent with interaction of a refractory harzburgite protolith with a high-Mg no. melt at depth (resulting in the formation of coarse-grained clinopyroxene-rich lherzolite and wehrlite) and with a low-Mg no. evolved melt in the shallow subcontinental lithospheric mantle (forming fine-grained harzburgite). We propose that pervasive melt–peridotite reaction – promoted by lateral and/or near-vertical mantle flow associated with lithospheric tearing – resulted in the synkinematic crystallization of secondary lherzolite and wehrlite and had a key effect on grain size reduction during the operation of the Tell–Rif STEP fault. Melt–rock reaction and secondary formation of lherzolite and wehrlite may be widespread in other STEP fault systems worldwide.

scholarly journals Lithosphere tearing along STEP faults and synkinematic formation of lherzolite and wehrlite in the shallow subcontinental mantle

2019 ◽  
Author(s):  
Károly Hidas ◽  
Carlos J. Garrido ◽  
Guillermo Booth-Rea ◽  
Claudio Marchesi ◽  
Jean-Louis Bodinier ◽  
...  
Keyword(s):  
Grain Size ◽  
Lithospheric Mantle ◽  
Volcanic Field ◽  
Mantle Xenoliths ◽  
Coarse Grained ◽  
Fault System ◽  
Mantle Flow ◽  
Second Phase ◽  
Fine Grained ◽  
Wide Range

Abstract. Subduction-Transform Edge Propagator (STEP) faults are the locus of continual lithospheric tearing at slab edges, resulting in sharp changes in the lithospheric and crustal thickness and triggering lateral and/or near-vertical mantle flow. However, the mechanisms at the lithospheric mantle scale are still poorly understood. Here, we present the microstructural study of olivine-rich lherzolite, harzburgite and wehrlite mantle xenoliths from the Oran volcanic field (Tell Atlas, NW Algeria). This alkali volcanic field occurs along a major STEP fault responsible for the Miocene westward slab retreat in the westernmost Mediterranean. Mantle xenoliths provide a unique opportunity to investigate the microstructures in the mantle section of a STEP fault system. The microstructures of mantle xenoliths show a variable grain size ranging from coarse granular to fine-grained equigranular textures uncorrelated with modal variations. The major element composition of the mantle peridotites provides temperature estimates in a wide range (790–1165 °C) but in general, the coarse-grained and fine-grained peridotites suggest deeper and shallower provenance depth, respectively. Olivine grain size in the fine-grained peridotites depends on the size and volume fraction of the pyroxene grains, which is consistent with pinning of olivine grain growth by pyroxenes as second phase particles. In the coarse-grained peridotites, well-developed olivine crystal preferred orientation (CPO) is characterized by orthorhombic and [100]-fiber symmetries, and orthopyroxene has a coherent CPO with that of olivine, suggesting their coeval deformation by dislocation creep at high-temperature. In the fine-grained microstructures, along with the weakening of the fabric strength, olivine CPO symmetry exhibits a shift towards [010]-fiber and the [010]- and [001]-axes of orthopyroxene are generally distributed subparallel to those of olivine. These data are consistent with deformation of olivine in the presence of low amounts of melts and the precipitation of orthopyroxenes from a melt phase. The bulk CPO of clinopyroxene mimics that of orthopyroxene via a topotaxial relationship of the two pyroxenes. This observation points to a melt-related origin of most clinopyroxenes in the Oran mantle xenoliths. The textural and geochemical record of the peridotites are consistent with interaction of a refractory harzburgite protolith with a high-Mg# melt at depth (resulting in the formation of coarse-grained clinopyroxene-rich lherzolite and wehrlite), and with a low-Mg# evolved melt in the shallow subcontinental lithospheric mantle (forming fine-grained harzburgite). We propose that pervasive melt-peridotite reaction – promoted by lateral and/or near-vertical mantle flow associated with lithospheric tearing – resulted in the synkinematic crystallization of secondary lherzolite and wehrlite and played a key effect on grain size reduction during the operation of the Rif-Tell STEP fault. Melt-rock reaction and secondary formation of lherzolite and wehrlite may be widespread in other STEP fault systems worldwide.

Decoupled water and iron enrichments in the cratonic mantle: A study on peridotite xenoliths from Tok, SE Siberian Craton

2020 ◽  
Vol 105 (6) ◽  
pp. 803-819
Author(s):  
Luc S. Doucet ◽  
Yongjiang Xu ◽  
Delphine Klaessens ◽  
Hejiu Hui ◽  
Dmitri A. Ionov ◽  
...  
Keyword(s):  
Water Content ◽  
Siberian Craton ◽  
Lithospheric Mantle ◽  
Large Scale ◽  
Basaltic Magma ◽  
Mantle Xenoliths ◽  
Spinel Peridotite ◽  
Peridotite Xenoliths ◽  
Cratonic Mantle ◽  
Water Contents

Abstract Water and iron are believed to be key constituents controlling the strength and density of the lithosphere and, therefore, play a crucial role in the long-term stability of cratons. On the other hand, metasomatism can modify the water and iron abundances in the mantle and possibly triggers thermo-mechanical erosion of cratonic keels. Whether local or large scale processes control water distribution in cratonic mantle remains unclear, calling for further investigation. Spinel peridotite xenoliths in alkali basalts of the Cenozoic Tok volcanic field sampled the lithospheric mantle beneath the southeastern margin of the Siberian Craton. The absence of garnet-bearing peridotite among the xenoliths, together with voluminous eruptions of basaltic magma, suggests that the craton margin, in contrast to the central part, lost its deep keel. The Tok peridotites experienced extensive and complex metasomatic reworking by evolved, Ca-Fe-rich liquids that transformed refractory harzburgite to lherzolite and wehrlite. We used polarized Fourier transform infrared spectroscopy (FTIR) to obtain water content in olivine, orthopyroxene (Opx), and clinopyroxene (Cpx) of 14 Tok xenoliths. Olivine, with a water content of 0–3 ppm H2O, was severely degassed, probably during emplacement and cooling of the host lava flow. Orthopyroxene (49–106 ppm H2O) and clinopyroxene (97–300 ppm H2O) are in equilibrium. The cores of the pyroxene grains, unlike olivine, experienced no water loss due to dehydration or addition attributable to interaction with the host magma. The water contents of Opx and Cpx are similar to those from the Kaapvaal, Tanzania, and North China cratons, but the Tok Opx has less water than previously studied Opx from the central Siberian craton (Udachnaya, 28–301 ppm; average 138 ppm). Melting models suggest that the water contents of Tok peridotites are higher than in melting residues, and argue for a post-melting (metasomatic) origin. Moreover, the water contents in Opx and Cpx of Tok peridotites are decoupled from iron enrichments or other indicators of melt metasomatism (e.g., CaO and P2O5). Such decoupling is not seen in the Udachnaya and Kaapvaal peridotites but is similar to observations on Tanzanian peridotites. Our data suggest that iron enrichments in the southeastern Siberian craton mantle preceded water enrichment. Pervasive and large-scale, iron enrichment in the lithospheric mantle may strongly increase its density and initiate a thermo-magmatic erosion. By contrast, the distribution of water in xenoliths is relatively “recent” and was controlled by local metasomatic processes that operate shortly before the volcanic eruption. Hence, water abundances in minerals of Tok mantle xenoliths appear to represent a snapshot of water in the vicinity of the xenolith source regions.

scholarly journals Geochemistry of noble gas and CO2 in fluid inclusions from lithospheric mantle beneath Eifel and Siebengebirge (Germany)

2020 ◽  
Author(s):  
Andrea Luca Rizzo ◽  
Massimo Coltorti ◽  
Barbara Faccini ◽  
Federico Casetta ◽  
Theodoros Ntaflos ◽  
...  
Keyword(s):  
Fluid Inclusions ◽  
Lithospheric Mantle ◽  
Noble Gas ◽  
Mantle Xenoliths ◽  
Gas Content ◽  
Great Opportunity ◽  
Chem Geol ◽  
Wide Range ◽  
Eruptive Centers ◽  
West Eifel

<p>The study of fluid inclusions (FI) composition (He, Ne, Ar, CO<sub>2</sub>) integrated with the petrography and mineral chemistry of mantle xenoliths representative of the Sub Continental Lithospheric Mantle (SCLM) is a unique opportunity for constraining its geochemical features and evaluating the processes and the evolution that modified its original composition. An additional benefit of this type of studies is the possibility of better constraining the composition of fluids rising through the crust and used for volcanic or seismic monitoring.  </p><p>In this respect, the volcanic areas of Eifel and Siebengebirge in Germany represent a great opportunity to test this scientific approach for three main reasons. First, these volcanic centers developed in the core of the Central European Volcanic Province where it is debated whether the continental rift was triggered by a plume (Ritter, 2007 and references therein). Second, Eifel and Siebengebirge formed in Quaternary (0.5-0.01 Ma) and Tertiary (30-6 Ma), respectively, thus spanning a wide range of age. Third, Eifel is characterized by the presence of CO<sub>2</sub>-dominated gas emissions and weak earthquakes that testify that local magmatic activity is nowadays dormant, but not ended (e.g., Bräuer et al., 2013). It is thus important to better constrain the noble gas signature expected in surface gases in case of magmatic unrest.</p><p>This work focuses on the petrological and geochemical study of mantle xenoliths sampled in the West Eifel and Siebengebirge volcanic areas (Germany) and aims at enlarging the knowledge of the local SCLM. Gautheron et al. (2005) carried out the first characterization of noble gases in FI of crystals analyzed by crushing technique (as in our study) but limited to olivines and to West Eifel eruptive centers. Here, we integrate that study by analyzing olivines, orthopyroxenes and clinopyroxenes from a new suite of samples and by including two eruptive centers from Siebengebirge volcanic field (Siebengebirge and Eulenberg quarries).</p><p>Xenoliths from the Siebengebirge localities are characterized by the highest Mg# for olivine, clinopyroxene and Cr# for spinel, together with the lowest Al<sub>2</sub>O<sub>3</sub> contents for both pyroxenes, suggesting  that the mantle beneath Siebengebirge experienced high degree of melt extraction (up to 30%) while metasomatic/refertilization events were more efficient in the mantle beneath West Eifel.</p><p>In terms of CO<sub>2</sub> and noble gas concentration, clinopyroxene and most of the orthopyroxene show the highest gas content, while olivine are gas-poor. The <sup>3</sup>He/<sup>4</sup>He varies between 5.5 and 6.9 Ra. These values are comparable to previous measurements in West Eifel, mostly within the range proposed for European SCLM (6.3±0.4 Ra), and slightly below that of MORB (Mid-Ocean Ridge Basalts; 8±1Ra). The Ne and Ar isotope ratios fall along a binary mixing trend between air and MORB-like mantle. He/Ar* in FI and Mg# and Al<sub>2</sub>O<sub>3</sub> content in minerals confirm that the mantle beneath Siebengebirge experienced the highest degree of melting, while the metasomatic/refertilization events largely affected the Eifel area.</p><p>References</p><p>Bräuer, K., et al. 2013. Chem. Geol. 356, 193–208.</p><p>Gautheron, C., et al. 2005. Chem. Geol. 217, 97–112.</p><p>Ritter, J.R.R., 2007. In: Ritter, J.R.R., Christensen, U.R. (Eds.), Mantle Plumes: A Multidisciplinary Approach. Springer-Verlag, Berlin Heidelberg, pp. 379–404.</p>

scholarly journals The age and evolution of the lithospheric mantle in the East Antarctic Craton: osmium isotope composition and the distribution of the platinum group elements in spinel lherzolite nodules

2019 ◽  
Vol 485 (6) ◽  
pp. 726-731
Author(s):  
R. Sh. Krymsky ◽  
A. V. Antonov ◽  
B. V. Belyatsky ◽  
N. M. Sushchevskaya ◽  
S. A. Sergeev
Keyword(s):  
Lithospheric Mantle ◽  
Isotope Composition ◽  
Platinum Group Elements ◽  
Mantle Xenoliths ◽  
Spinel Lherzolite ◽  
Thermal Erosion ◽  
Rift Propagation ◽  
Mantle Section ◽  
Partial Destruction ◽  
Osmium Isotope

The mantle xenoliths of lherzolite composition from Mesozoic alkaline-ultrabasic diatremes of the Jetty Oasis were studied. The studied xenoliths represent the mantle section of the East Antarctic Craton down to depths of 60-80 km. The osmium isotope composition of these nodules testifies to the beginning of the formation of the lithospheric mantle in the considered region at about 2400 Ma. The absence of any signs of Early Archean lithosphere points either to partial destruction of the lithosphere at the convergent boundary of the plates in the Late Archean or to thermal erosion of the Archean lithosphere under the deep-seated plume impact at the Mesozoic time during rift propagation.

scholarly journals Thermal State, Thickness, and Composition of the Lithospheric Mantle beneath the Upper Muna Kimberlite Field (Siberian Craton) Constrained by Clinopyroxene Xenocrysts and Comparison with Daldyn and Mirny Fields

Minerals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 549 ◽  
Author(s):  
Anna M. Dymshits ◽  
Igor S. Sharygin ◽  
Vladimir G. Malkovets ◽  
Igor V. Yakovlev ◽  
Anastasia A. Gibsher ◽  
...  
Keyword(s):  
Steady State ◽  
Siberian Craton ◽  
Lithospheric Mantle ◽  
Thermal State ◽  
Early Carboniferous ◽  
Mantle Xenoliths ◽  
Lithospheric Thickness ◽  
Lithosphere Thickness ◽  
The One ◽  
Kimberlite Field

To gain better insight into the thermal state and composition of the lithospheric mantle beneath the Upper Muna kimberlite field (Siberian craton), a suite of 323 clinopyroxene xenocrysts and 10 mantle xenoliths from the Komsomolskaya-Magnitnaya (KM) pipe have been studied. We selected 188 clinopyroxene grains suitable for precise pressure (P)-temperature (T) estimation using single-clinopyroxene thermobarometry. The majority of P-T points lie along a narrow, elongated field in P-T space with a cluster of high-T and high-P points above 1300 °C, which deviates from the main P-T trend. The latter points may record a thermal event associated with kimberlite magmatism (a “stepped” or “kinked” geotherm). In order to eliminate these factors, the steady-state mantle paleogeotherm for the KM pipe at the time of initiation of kimberlite magmatism (Late Devonian–Early Carboniferous) was constrained by numerical fitting of P-T points below T = 1200 °C. The obtained mantle paleogeotherm is similar to the one from the nearby Novinka pipe, corresponding to a ~34–35 mW/m2 surface heat flux, 225–230 km lithospheric thickness, and 110–120 thick “diamond window” for the Upper Muna field. Coarse peridotite xenoliths are consistent in their P-T estimates with the steady-state mantle paleogeotherm derived from clinopyroxene xenocrysts, whereas porphyroclastic ones plot within the cluster of high-T and high-P clinopyroxene xenocrysts. Discrimination using Cr2O3 demonstrates that peridotitic clinopyroxene xenocrysts are prevalent (89%) among all studied 323 xenocrysts, suggesting that the Upper Muna mantle is predominantly composed of peridotites. Clinopyroxene-poor or -free peridotitic rocks such as harzburgites and dunites may be evident at depths of 140–180 km in the Upper Muna mantle. Judging solely from the thermal considerations and the thickness of the lithosphere, the KM and Novinka pipes should have excellent diamond potential. However, all pipes in the Upper Muna field have low diamond grades (<0.9, in carats/ton), although the lithosphere thickness is almost similar to the values obtained for the high-grade Udachnaya and Mir pipes from the Daldyn and Mirny fields, respectively. Therefore, other factors have affected the diamond grade of the Upper Muna kimberlite field.

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